In a display device such as cathode ray tube display device (CRT), plasma display panel (PDP), electroluminescence display (ELD) and liquid crystal display device (LCD), an antireflection film as an optical functional film is generally disposed on the outermost surface of the display to reduce the reflectance by using the principle of optical interference and thereby prevent the external light reflection which causes reduction in contrast or projection of an image.
Such an antireflection film can be generally produced by forming a low refractive index layer of an appropriate thickness on a support, in which the refractive index of the low refractive index layer is lower than that of the support. In order to realize a low reflectance, a material having a refractive index as low as possible is preferably used for the low refractive index layer. Furthermore, since the antireflection film is used on the outermost surface of a display, this film is required to have high scratch resistance. In order to realize high scratch resistance of a thin film with a thickness of about 100 nm, strength of the film itself and tight adhesion to the underlying layer are necessary.
With recent trend toward thin and large displays, the antireflection film is required to have a wide area and a uniform surface state. Also increase in the productivity of antireflection film is demanded in view of cost reduction and for this purpose, high-rate coating is an essential technique. However, the high-rate coating is liable to cause film thickness unevenness due to associated wind or drying air and the surface state uniformity required of the antireflection film can be hardly maintained. The “surface state uniformity” as used herein means that fluctuation in the optical performances represented by antireflection and in the film properties such as scratch resistance is small in the entire display part of a display.
The film thickness unevenness accompanying the high-rate coating is known to be effectively improved by enhancing the leveling property of the coating solution. One technique heretofore proposed for enhancing the leveling property is a method of adding a surfactant in the coating solution. This method is based on the mechanism that when a surfactant is added in the coating solution, the surface tension decreases to improve the wetting to a material on which the coating-solution is coated, and the change of surface tension in the process of forming a coating film is made small or reduced to prevent heat convection and thereby improve the film uniformity (see, Haruo Kiryu (supervisor), Coating Yo Tenka Zai no Saishin Gijutsu (Up-to-date Technology of Additives for Coating), CMC (0.2001)).
JP-A-2002-249706 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses a case where excellent leveling property can be realized by using a fluorine-base polymer-type surfactant containing a perfluoroalkyl group having 6 or less carbon atoms. However, when the coating is performed by using a fluorine-base surfactant, a uniform film may be formed by virtue of its leveling effect, but the surface free energy of the coating film formed after drying decreases and this causes a problem that when another material is laminated on the coating film surface or coating is further applied thereon, the adhesion at the interface is weak and the scratch resistance becomes bad.